This disclosure pertains to microlithography, which is a process by which a pattern is transferred from a mask or reticle to a lithographic substrate, such as a semiconductor wafer, using an energy beam. More specifically, the disclosure pertains to microlithography performed using a charged particle beam such as an electron beam or ion beam. Even more specifically, this disclosure pertains to robotic manipulators used in conjunction with charged-particle-beam (CPB) microlithography systems for, e.g., moving reticles and substrates into and out of position for exposure.
Conventional CPB microlithography systems typically include at least one robotic manipulator used for conveying pattern-defining reticles or masks (termed xe2x80x9creticlesxe2x80x9d herein) and/or lithographic substrates into and out of position for exposure. Robotic manipulators are highly desirable over manual manipulation of these objects for many reasons, including rapidity and consistency of operation as well as cleanliness, etc. For example, a robotic manipulator usually is used for moving semiconductor wafers, coated with resist, from a wafer cassette to a substrate stage on which the substrates are exposed individually and for moving exposed substrates to cassette that holds exposed wafers. A robotic manipulator also is used for moving reticles from a reticle cassette to a reticle stage, on which the reticles are held individually for exposure, and for moving reticles, after use for exposure, back to the reticle cassette. In a CPB microlithography system, these conveying motions performed by the respective robotic manipulators include motions into and out of vacuum chambers, which involves motions into and out of load-lock chambers, gate valves between chambers, and the like. Typically, the entire motion sequence for reticles and wafers is completely automated to avoid any direct human contact with the substrates and reticles. A typical robotic manipulator includes a moving member, such as an arm, as well as machine components such as ball screws and bearings. For maximal durability, these various components conventionally are made of metal, more specifically magnetic metal.
For maximal xe2x80x9cthroughputxe2x80x9d (i.e., number of substrates that can be processed microlithographically per unit time), motions of reticles and substrates by the robotic manipulators usually occur while lithographic exposures are being performed simultaneously, at least to some degree. However, as a manipulator made of magnetic material is operated so as to cause movement of a part of the manipulator, the manipulator produces a moving xe2x80x9cstrayxe2x80x9d magnetic field. If the moving part of the manipulator is located near an exposure location or near the trajectory of the charged particle beam, the moving magnetic field can cause a significant perturbation of the beam trajectory and/or exposure fidelity, which typically results in a distortion or other imaging fault of the pattern as actually formed on the resist-coated substrate.
Exemplary stray magnetic fields generated in this manner include direct-current (DC) disturbances originating in the magnetic materials of motors built into the manipulators, direct-current/alternating-current (DC/AC) disturbances generated by electrical currents flowing to and from the manipulator, and DC/AC disturbances generated during actuation of the manipulator. Among these various disturbances, a particularly large disturbance is manifest in the magnetic-field fluctuations caused by movement of magnetic materials such as the arm of a robotic manipulator during actuation of the manipulator.
Microlithographic exposures typically occur at or near the optical axis of the CPB microlithography system. In such systems (e.g., electron-beam microlithography systems), a stray magnetic field (e.g., as generated by a motor or other source in a robotic manipulator) has a magnitude that decreases in inverse proportion to the square of the distance between the source of the field and the optical axis. With robotic manipulators having a wide range of arm motion, the effects of stray magnetic fields conventionally are reduced by installing the xe2x80x9cmain unitxe2x80x9d (containing motors and the like) of the manipulator at a maximal distance from the optical axis. However, if the arm itself is made of a magnetic material, then significant magnetic-field fluctuations affecting the beam trajectory tend to occur regardless of the distance between the main unit and the optical axis. These effects arise due to the rather large operational range of the arm and to the arm closely approaching the optical axis at least during some of its motions.
Plots of magnetic-field intensity (B) resulting from representative movements of a conventional robotic manipulator are shown in FIG. 3, in which the ordinate is output in volts and the abscissa is time (sec). The plots were generated by periodically moving the robotic manipulator in the vertical (Z) direction while measuring magnetic-field intensity B at a location that is separated by approximately 300 mm from the center position of the manipulator. Sensor output was in volts. In this example the manipulator was made of a magnetic stainless steel. Measurements of the magnetic-field intensity were performed using a 3-axis DC sensor (DC to approximately 5 Hz, resolution 5 xcexcGauss). The solid-line plot denotes magnetic-field intensity (Bx) in the X-direction at the measurement point; the dot-dashed line denotes magnetic-field intensity (By) in the Y-direction at the measurement point; and the dashed line denotes magnetic-field intensity (Bz) in the Z-direction at the measurement point.
FIG. 3 indicates that vertical (Z-direction) movement of the robot produces a magnetic-field fluctuation of approximately 6.8 mG in the X-direction, approximately 2.0 mG in the Y-direction, and approximately 0.4 mG in the Z-direction. Conventionally, active magnetic-field cancellers have been used for reducing the magnitude of these magnetic-field disturbances. An xe2x80x9cactivexe2x80x9d magnetic-field canceller comprises an energizable component such as a Helmholtz coil or the like in surrounding relationship to a field-vulnerable portion of the microlithography system. The Helmholtz coil is energized in a controllable manner by a coil-energization circuit. The active canceller also includes a Gauss meter situated and configured to measure the magnitude of a potentially disturbing magnetic field in the vicinity of the field-vulnerable portion and to provide data regarding the detected field to the coil-energization circuit in a feedback manner. Thus, the coil-energization circuit supplies electrical current to the Helmholtz coil based on field measurements obtained by the Gauss meter. In response to a detected magnetic field that potentially could disturb the beam, the Helmholtz coil generates a countervailing magnetic field having a magnitude equal to that of the detected field but a direction opposite the direction of the detected field. As a result, the detected field is canceled.
Due to the high intensity and wide distribution of the magnetic field produced by Helmholtz coils and to limitations on the size of the Gauss meter, it is difficult to install the Gauss meter in a confined space (xe2x80x9ctarget spacexe2x80x9d) in which magnetic-field cancellation is desired and to achieve ideal field cancellation. To solve this problem one or more small correcting coils conventionally are situated in the vicinity of the Gauss meter. The correcting coils are used for correcting deviations of the magnetic field between the actual installation position of the Gauss meter and the target space. Unfortunately, the correcting coils and Helmholtz coils are fixed in position. Use of a robotic manipulator that generates beam-disturbing magnetic fields requires use of multiple corrective-field-generation sources that are operated sequentially. As a result, the magnetic field at the location of the Gauss meter frequently does not correspond with the magnetic field of the target space on a one-to-one basis, resulting in substantial difficulty in canceling the potentially disturbing magnetic field accurately.
According to a first aspect of the invention, charged-particle-beam (CPB) microlithography systems are provided. An embodiment of such a system comprises a CPB optical system situated and configured to irradiate a charged particle beam onto an exposure-sensitive surface of a lithographic substrate so as to transfer and imprint a resolved pattern on the exposure-sensitive surface. The system also includes a first robotic manipulator situated relative to the CPB optical system and configured for conveying an object relative to the CPB optical system. The first robotic manipulator comprises at least one moving member that moves, during actuation of the manipulator, relative to the CPB optical system. The at least one moving member is substantially non-magnetic, as defined herein.
By way of example, the first robotic manipulator can be configured to convey a reticle to a reticle stage for exposure and from the reticle stage after exposure. As another example, the first robotic manipulator can be configured to convey a lithographic substrate to a substrate stage for exposure and from the substrate stage after exposure.
Typically, the first robotic manipulator comprises multiple moving members including a first arm member and an object-holding member pivotably attached to the first arm member. In this configuration the object-holding member is used for holding the object as the first robotic manipulator moves the object in a vicinity of a magnetic field produced by the CPB optical system, and the first arm member and the holding member are each made of a substantially non-magnetic material (i.e., a material having a relative magnetic permeability of 1.0005 or less). In this regard, the non-magnetic material can be, for example, Ti or SiC or other material having the stated relative magnetic permeability.
The moving members of the first robotic manipulator also can include a first shaft pivotably coupling the object-holding member to the first arm member, wherein the first shaft is made of a substantially non-magnetic material. The multiple members also can include a second arm member and a second shaft connecting the first and second arm members together in a manner allowing the first arm member to pivot about the second shaft relative to the second arm member in response to actuation of the first robotic manipulator. In this configuration the second arm member and second shaft are each made of a substantially non-magnetic material.
The CPB optical system typically is contained inside a vacuum process chamber to which is connected at least a load chamber through which objects are transferred into and out of the vacuum process chamber. In this configuration the first robotic manipulator desirably is configured, when actuated, to move the object from the load chamber to the vacuum process chamber and from the vacuum process chamber to the load chamber. The load chamber can be connected to a load-lock chamber. In this latter configuration the first robotic manipulator desirably is configured to move, when actuated, the object from the load-lock chamber to the load chamber, from the load chamber to the vacuum process chamber, from the vacuum process chamber to the load chamber, and from the load chamber to the load-lock chamber. Also, desirably, the first robotic manipulator is located inside the load chamber.
If the vacuum process chamber comprises an optical column containing an illumination-optical system and a reticle stage, the first robotic manipulator desirably is configured to move, when actuated, a reticle relative to the illumination-optical system. This movement is from the load-lock chamber to the load chamber, from the load chamber to the reticle stage, from the reticle stage to the load chamber, and from the load chamber to the load-lock chamber. This configuration can include a second robotic manipulator situated and configured to move, when actuated, the reticle relative to the illumination-optical system. This latter movement is from an external environment to the load-lock chamber and from the load-lock chamber to the external environment. The second robotic manipulator comprises at least one moving member that moves, during actuation of the second robotic manipulator, relative to the illumination-optical system, wherein the at least one moving member is substantially non-magnetic.
If the vacuum chamber comprises a wafer chamber containing a projection-optical system and a substrate stage, the first robotic manipulator desirably is configured to move, when actuated, a lithographic substrate relative to the projection-optical system. This movement is from the load-lock chamber to the load chamber, from the load chamber to the substrate stage, from the substrate stage to the load chamber, and from the load chamber to the load-lock chamber. This configuration can include a second robotic manipulator situated and configured to move, when actuated, the substrate relative to the projection-optical system. This latter movement is from an external environment to the load-lock chamber and from the load-lock chamber to the external environment. The second robotic manipulator comprises at least one moving member that moves, during actuation of the second robotic manipulator, relative to the projection-optical system, wherein the at least one moving member is substantially non-magnetic.
If the CPB microlithography system has a first robotic manipulator used for transferring a substrate relative to a projection-optical system, the microlithography system can include a second robotic manipulator used for transferring a pattern-defining reticle. In this configuration the vacuum process chamber further comprises an optical column containing an illumination-optical system and a reticle stage, to which optical column are connected a second load chamber and a second load-lock chamber. The second robotic manipulator in this embodiment is configured to move, when actuated, a reticle relative to the illumination-optical system. This movement is from the second load-lock chamber to the second load chamber, from the second load chamber to the reticle stage, from the reticle stage to the second load chamber, and from the second load chamber to the second load-lock chamber.
Another embodiment of a CPB microlithography system comprises a first vacuum process chamber containing an illumination-optical system and reticle stage. A first load chamber is connected to the first vacuum process chamber, and a first robotic manipulator is situated and configured to move, when actuated, a reticle relative to the illumination-optical system. This movement includes movement from the first load chamber to the reticle stage in the first vacuum process chamber, and from the reticle stage to the first load chamber. The first robotic manipulator comprises moving members that are substantially non-magnetic. The CPB microlithography system of this embodiment also includes a second vacuum process chamber containing a projection-optical system and substrate stage. A second load chamber is connected to the second vacuum process chamber, and a second robotic manipulator is situated and configured to move, when actuated, a substrate relative to the projection-optical system. This movement includes movement from the second load chamber to the substrate stage in the second vacuum process chamber, and from the substrate stage to the second load chamber. The second robotic manipulator comprises moving members that are substantially non-magnetic.
In this embodiment the respective moving members of the first and second robotic manipulators are made of a material such as any of the specific materials listed earlier above.
The CPB microlithography system further can comprise a first load-lock chamber connected to the first load chamber and a second load-lock chamber connected to the second load chamber. In this configuration the first robotic manipulator can be further configured to move, when actuated, the reticle from the first load-lock chamber to the first load chamber and from the first load chamber to the first load-lock chamber. The second robotic manipulator can be further configured to move the substrate from the second load-lock chamber to the second load chamber and from the second load chamber to the second load-lock chamber. Desirably, the first robotic manipulator is located in the first load chamber, and the second robotic manipulator is located in the second load chamber.
This CPB microlithography system further can comprise a third robotic manipulator situated and configured to move, when actuated, the reticle from an external environment to inside the first load-lock chamber and from the first load-lock chamber to the external environment, and a fourth robotic manipulator situated and configured to move, when actuated, the substrate from the external environment to inside the second load-lock chamber and from the second load-lock chamber to the external environment. The third and fourth robotic manipulators each comprise respective moving members that are substantially non-magnetic. To such end the respective moving members of the third and fourth robotic manipulators desirably are made of a material such as any of the materials listed earlier above. Similarly, the respective moving members of the first and second robotic manipulators are made of a substantially non-magnetic material such as one or more of the materials listed earlier above.
Another aspect of the invention is set forth in the context of a CPB microlithography method in which a charged particle beam is directed through a CPB optical system that produces a beam-controlling magnetic field so as to imprint a pattern on an exposure-sensitive surface of a lithographic substrate. In this context methods are provided for conveying an object relative to the CPB optical system without causing a significant perturbation of the beam-controlling magnetic field. An embodiment of such a method comprises the step of placing the object on a moving member of a robotic manipulator situated relative to the CPB optical system and configured for conveying an object relative to the CPB optical system. The moving member is substantially non-magnetic. The robotic manipulator is actuated so as to move the object relative to the CPB optical system.
If, by way of example, the object is a reticle, the CPB optical system can comprise an illumination-optical system, wherein actuation of the robotic manipulator also moves the reticle relative to the illumination-optical system. Actuation of the robotic manipulator also can result in placement of the reticle on a reticle stage of the illumination-optical system and removing the reticle from the reticle stage.
If, by way of another example, the object is a substrate, the CPB optical system can comprise a projection-optical system, wherein actuation of the robotic manipulator also moves the substrate relative to the projection-optical system. Actuation of the robotic manipulator also can result in placement of the substrate on a substrate stage of the projection-optical system and removing the substrate from the substrate stage.
These actuations of the robotic manipulator can be performed while performing a lithographic exposure. By making the moving member(s) of the robotic manipulator substantially non-magnetic, movements of the moving member(s) during lithographic exposure does not produce significant fluctuation of the magnetic field controlling the beam during exposure. This eliminates the need to perform movements of the reticle and substrate, for example, only during times in which exposures are not being made. Consequently, throughput is increased over conventional apparatus and methods, without sacrificing exposure accuracy.
The foregoing and additional features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.